Existing modelThe Mercury 55 features a newly developed active suspension platform: patent-pending ergoACTIV XP suspension with OpenAir back panel. What does this mean? Essentially these packs use the pivoting hip belt/floating shoulder strap ergoACTIV technology that you are already familiar with, the new ergoACTIV XP technology takes that ergoACTIV suspension platform and adapts it to heavier loads needed for full featured, multi-day backpacking trips. The hip belt on this suspension uses the 3D ball joint found on the ergoACTIV packs and adds urethane elastomers in the waist belt for more stability and dynamic load transfer.